Reduction of sulphate minerals and briquettes therefor



tltll Patented w th H, llhfldo ELIOT BOOGIE AND Jl'OfiIE'dPH JP. ROLLER,F WILMINGTON, DELAWARE, AS- SIGNORS T0 1E. T. DU JPONT DE NEMO'URS doCOMPANY, OT WTJLMTNGTUN, DELA- WARE, A. 'COEJPURATION 01E DELAWARE.

REDUCTIU N 01E SULPHA'TE MINERALS AND BRIQUETTES THEREJFUJEL ItoDrawing.

This invention relates to the production of alkali-metal, and alkalineearth metal, sulphides by the reduction of the corresponding sulphates,and While it applies particularly to the production of barium sulphide,it is also applicable to other sulphides such as those of calcium,strontium, and sodium. It has for its object an improven'icnt in themethod of carrying out this process for producing such sulphides.

According to the customary practice for the production of bariumsulphide, which is typical of the other alkaline earth sulphides, thefinely ground barytes (barium sulphate mineral) is mixed with more orless finely ground reducing material, such as coal or other carbonaceousmaterial. The propor tion of coal to mineral is generally 1 to 4, whichis in excess of that theoretically 1equired by the reaction. The averagefineness of the mineralis generally to 100 mesh. The charge in this formis fed into a suitable furnace, the operation being of the batch type,where it is heated to a red heat or higher, which effects the reductionof the barium sulphate to barium sulphide. The resulting product knownas black ash contams barium in the forms of the sulphide, of theunconverted barium sulphate, and of barium rendered unavailable due tothe deleterious reactions also occurring in the furnacing operation.

The furnace usually employed is of the rotating reverberatory type, from92 0 feet in length, and 6-10 feetin diameter, directly heated by acoal'grate, oil or gas burner at one end; but other types of furnacesare occasionally used, heated either by direct contact with combustionproducts or by heat transfer through an intervening wall,

Our invention is especially advantageous where the furnacing operationis continuous and involves direct contact of hot products of combustionwith the barytes to be reduced, as is the case in the customary methodabove described.

it has long been recognized that silica, which is universally present inbarytes ores, is an objectionable constituent, so that, in the mining oithe barytes, as much silica is removed as is practicable without toogreat an increase in the cost of the mining and refining of the mineral.For the production of sul- I phides it has heretofore been considerednee-- Application filed November 10, 19%. Serial No. 7429,05Bt.

essary to use a high grade barytes ore, that. is, one having less than4% of silica. A high grade barytcs mineral may also be defined as amineral containing 94% or more of barium Y sulphate, about half theimpurities consisting of silica. The low grade mineral run down to wellunder 90% of barium sulphate and contain more than 4% of silica. Thereason for this demand for a mineral containing more than 94% bariumsulphate, is the poor yield, running in some cases less than which isobtained with mineral containing substantially more than 4% sili a. As aresult, the comparatively large deposits of low grade mineral haveheretofore been practically unavailable as a source of supply for theprbduction oft'barium sulphidea compound which is used in enormousquantities in the production of the white pigment, lithopone.

Uur invention is based to a great extent upon the discovery that wherethe sulphate mineral is heated by direct contact with hot products ofcombustion, these hot products have a deleterious action on the furnacecharge: this deleterious action seems to be due, at least in part, to anacceleration of the chemical reaction between the barium and the silica,and is accentuated when the degree of subdivision of the charge isincreased probably because (it the greater surface which is therebyexposed to the hot gases.

Our invention consists in preventing these hot products of combustionfrom contacting with a great proportion of the furnace charge in so faras is compatible with the ellicient handling and heating of such charge.This we do by first molding or pressing the furnace charge into the formof small dense masses, tablets or briquettes which are relativelyimpervious to the hot combustion gases, and which have suti'icieutcoherence to retain their shape throughout the furnacing operation. Forproper handling these masses should be less than four inches in diameteror length, and are preferably of from one-halt to two inches in diameterand/or length. Small masses or tablets substantially less than one-halfinch in diameter expose more surface to the chemical action of the hotgases than is desirable. Briquettes having one or more dimensions inexcessv of four inches may of course be used, and come Within the scopeout our invention, but no special advantage is gained by this increasein S t tit) ltltl By subjecting the furnace charge in this form to hotcombustion products, the tablets or briquettes are easily brought to thetemperature required for the reduction of the sulphate by the powderedcoal in admixture therewith, while at the same time the proportion ofmineral which is subjected to the chemical action of these combustiongases 1s confined approximately to the surface layers of said tablets orbriquettes.

Although the increase in the yield of sulphide when using a high grademineral is sufficient to justify the use of our process withsuch'mineral, the outstanding importance of this new process is mostclearly demonstrated by the remarkable increase in yield which isobtained when it is used with a low grade mineral containing, say, from80 to 90% of barium sulphate and 8% or more of silica. A typicalillustration of this increased yield 1s give-n 1n the followlng table:

' Yield with Type of charge. Poor mineralA. Good mineral B. (B21804 89%.(81180 94 7,). 310 :1070.) s102 3%.)

Per cent. Per cent. Usual operation 60. 3 81. 5

Briquettes 7 dia.) 91.4 94.1

The furnacing conditions for our process are those ordinarily used inthe prior art, namely, a three-hour reduction period with the chargetemperature of from 950 to 1150 C.

The tablets or briquettes mentioned above may be prepared in various was, but we prefer the following procedure: ne part of coal and about fourparts of barytes mineral, each preferably ground or pulverized to afineness of 100 mesh, are thoroughly mixed together, and with theresulting mixture there is incorporated a suitable binding material suchas crude petroleum, sulphite process waste liquor, starch, molasses orother similar material. The resulting mass is then pressed in a suitablemold, preferably at a high pressure, into tablets or briquettes; thesemay have practically any form, although we prefer the pillow shape.

In addition to the prevention of direct contact of the combustionproducts with a large proportion of the furnace charge at very hightemperatures, an advantage of considerable importance in introducing thefurnace charge in the formof dense, compact masses results from the factthat the mineral and coal are tightly packed together, and re main inintimate contact throughout the furnacing operation, thus facilitatingthe reaction between the solid phases carbon and barium sulphate in themineral; and also from the fact that since contact with hot combastionproducts is confined to the surfaces of the tablets, the degree ofsubdivision of the mineral and coal before being mixed and molded may begreatly increased, thereby still further increasing the degree ofintimate contact of the'mlneral and coal while they are being subjectedto the high temperature required for reduction of sulphate to sulphide.

' Although throughout the above specification and following claims, wedescribe the furnace charge and the tablets or briquettes as consistingessentially of ore and coal, it will be understood that b the word coalwe mean to include any carbonaceous material whichwill function likecoal in effecting re-. duction of the sulphate to sulphide.

We claim:

1. The process of treating a low ado barytes ore containing more than 4%of silica to reduce the sulphate therein to sulphide, which comprisesmixing from four to six parts of finely powdered ore with about one partof finely powdered coal and with a binder, presslng the resultingmixture into tablets or briquettes, and bringing said tablets orbriquettes into contact with hot prod ucts of combustion until thereduction of the sulphate to sulphide is practically complete.

2. A process as set forth in claim 1 in which .the smallest-dimension ofthe tablets or briquettes is in excess of half an inch, and thetemperature to which they are heated is from about 950 to 1150 C.

3. As a new article, powdered sulphate ore containing more than 4% ofsilica and held together in the form of substantially non-porous tabletsor briquettes by asuitable binder, which depends upon its cokingproperties for its binding action.

4. As a new article, bar tes containing more than 4% of silica mixedwith powdered coal in the proportion of four to six of finely powderedore to one part of coal, and held together in the form of substantiallynonporous tablets or briquettes by a suitable binder, which depends uponits coking properties for its binding action.

5. As a. new article, barytes containing less than 90% of bariumsulphate and more than 4% of silica mixed with powdered coal in theproportion of four to six parts of finely powdered ore to one part ofcoal, and held together in the form of substantially nonporous tabletsor briquettes by a suitable binder, which depends upon its cokingproperties for its binding action.

In testimony whereof we aflix our signatures.

parts JAMES ELIOT ROUGE. JOSEPH P. KOLLER.

